At present, photovoltaic cells, also referred to as solar cells, are widely applied to absorb an incoming electromagnetic radiation, e.g. solar radiation, and convert it to electrical energy. Different types of photovoltaic cell designs currently exist which may comprise various light (in general, radiation) absorbing materials such as silicon (mono-crystalline, poly-crystalline or amorphous), GaAs, polymers, CdTe, . . . etc., each of the aforementioned materials having a unique absorption characteristic. Currently, most of the world's photovoltaic modules or cells comprise mono or polycrystalline silicon.
In order to operate, a photovoltaic cell requires a certain energy photon to separate an electron-hole pair. For silicon based cells, the required energy is equivalent to near IR (infrared) radiation. Photons having less energy than required, i.e. outside the absorption spectrum, are thus wasted by not being absorbed. Photons having more energy than required may waste the excess portion as heat. As a result, a comparatively large part of incoming radiation may not be used to generate electrical energy. It can further be stipulated that the amount of heat generated in a photovoltaic cell may further deteriorate the performance of the cell.
Different solutions have been devised to convert a larger portion of the incoming radiation spectrum into electrical energy.
As an example, it has been proposed to apply photovoltaic arrays having multiple cells with different required energies, so as to capture more of the solar spectrum efficiently. For such a solution, reference can e.g. be made to WO 2008/024201. WO 2008/024201 discloses the use of a spectral splitting assembly for splitting an incident light into multiple beams of light, each having a different nominal spectral bandwidth. By an appropriate spatial arrangement of multiple solar cells, responsive to the different nominal spectral bandwidth, an improved use of the incident light can be made. The arrangement as disclosed in WO 2008/024201 further describes the use of an optical concentrator for increasing the amount of incident light to the solar cells. A drawback of the arrangement as shown is that it required different types of solar cells, each responsive to a different spectral bandwidth and a spectral splitting assembly, making the arrangement rather expensive.
Similar solar cell arrangements that apply solar cells having different band gaps and dispersive optics capable of directing wavelengths of incoming lights to the most appropriate cell for those wavelengths are also described in US 2007/0277869.
To convert a larger portion of the incoming radiation spectrum into electrical energy it has also been proposed to coat a photovoltaic cell with a light conversion material, which convert an unusable part of the incoming spectrum into the required energy. Reference can e.g. be made to EP 1 865 562 for such an arrangement. A drawback of such a solution is that it provides a permanent conversion and is not adapted to accommodate for varying operating conditions of the solar cell. Such varying operating conditions may occur when solar cells are applied to power mobile devices. In such an application, the radiation spectrum of the incident light may vary, depending on the location (e.g. indoors or outdoors) where the device is used.
It may further be noted that the arrangements proposed in US 2007/0277869 or WO 2008/024201 are not adapted to accommodate for varying operating conditions either.